linux-kernel - Re: [PATCH -next] selinux: Fix potential memory leak in selinux_add

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Date:   Tue, 14 Jun 2022 09:18:34 +0800
From:   xiujianfeng <xiujianfeng@...wei.com>
To:     Paul Moore <paul@...l-moore.com>
CC:     <stephen.smalley.work@...il.com>, <eparis@...isplace.org>,
        <omosnace@...hat.com>, <selinux@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH -next] selinux: Fix potential memory leak in
 selinux_add_opt

Hi,

在 2022/6/14 4:22, Paul Moore 写道:
> On Sat, Jun 11, 2022 at 5:07 AM Xiu Jianfeng <xiujianfeng@...wei.com> wrote:
>> In the entry of selinux_add_opt, *mnt_opts may be assigned to new
>> allocated memory, and also may be freed and reset at the end of the
>> function. however, if security_context_str_to_sid failed, it returns
>> directly and skips the procedure for free and reset, even if it may be
>> handled at the caller of this function, It is better to handle it
>> inside.
>>
>> Fixes: 70f4169ab421 ("selinux: parse contexts for mount options early")
>> Signed-off-by: Xiu Jianfeng <xiujianfeng@...wei.com>
>> ---
>>   security/selinux/hooks.c | 12 +++++++-----
>>   1 file changed, 7 insertions(+), 5 deletions(-)
> Have you actually observed a memory leak from the selinux_mnt_opts
> allocation in selinux_add_opt()?
>
> The selinux_add_opt() function has two callers:
> selinux_sb_eat_lsm_opts() and selinux_fs_context_parse_param().  The
> former cleans up the selinux_mnt_opts allocation it its error handler
> while the latter will end up calling
> security_free_mnt_opts()/selinux_free_mnt_opts() to free the
> fs_context:security when the fs_context is destroyed.
>
> This patch shouldn't be necessary.

I may not have made it clear, I said potential means may have a third 
caller in the future. Anyway,

Yes, you are right,  currently no memleak here, because the two callers 
will do the cleanup, from this point of view,

I think the error handler as following is not necessary:

err:
         if (is_alloc_opts) {
                 kfree(opts);
                 *mnt_opts = NULL;
         }

otherwise, some error paths goto err label while others don't, It's 
confusing.